Originally Posted by
2W0EPI
So, a glow temperature controls the ignition timing glow style?, i.e. we can advance(hot) or retard(cold) as a 3(cold/medium/hot) position ignition timing control?
No... it does not work like that.... the complete story is long and complicated, but it basically comes down to that a given plug will, compared to a hotter or colder plug, retard or advance timing, but then the engine won't run right because actual timing
required is essentially a given, a "fixed value" so to speak. So you have to retune the needles, because mixture changes ALSO control ignition timing.
That retuning will basically return timing back to where it was before, with the previous plug.
Too lean mixtures lead to thermal runaways, too rich mixtures lead to waste and power loss. Compression ratio also changes timing, as well as Nitro percentages. Compression can be changed by adding or removing headshims (AKA "gaskets") and Nitro, obviously there are various mixes availlable, or you can mix your own if you have access to the ingredients.
These three factors need to be carefully balanced. The manual usually will tell you which fuel composition and which plug to use. You can experiment a little, but you should not stray too far from the manufacturers recommendations unless you have built up a suficient deal of experience with the matter.
Very crudely put: Fuel composition and Compression Ratio should be optimized for full power, and the plug heat grade is a bit of an experience thing: different grades result in differences in throttleability. A different plug will make the engine "run generally nicer" or not, is the best way to put it.
A "hot" plug does not have a higher temperature, that is a misconception. It either has a different alloy (stronger or weaker catalytic action) or a higher or lower heat retention (cooling down or retaining heat between the burn cycles).